Pollen Masses Research Articles

Pollination mechanism in Serapias with no pollinaria reconfiguration.

Orchidaceae, one of the most numerous families in the world's flora, have evolved various pollination strategies to favour cross-pollination, such as deceptive pollination and pollinarium reconfiguration. Among the terrestrial orchids of the Mediterranean, only species belonging to the genus Serapias show a strategy defined as shelter imitation. The floral elements form a tubular structure that insects use during their resting phases. The purpose of this article was to clarify the mechanisms that guarantee pollination with particular attention to the morphological interactions between orchids and pollinators and whether pollinaria reconfiguration is necessary in the promotion of cross-pollination in Serapias. Breeding system experiments and hand-pollination treatments indicated that Serapias was highly self-compatible, shows low value of natural fruit set and is pollinator limited. Time-lapse photos showed that the pollinarium had no refolding of the stipe or caudicle after its removal from the flower. The morphology of the flower determined the attack of the pollinarium on the occiput/vertex of insect. When the insect left the flower, the pollinarium was unable to encounter the stigma. When the insect made a second visit to another flower, the pollen masses of the first pollinarium ended up on the stigma and at the same time, the insect picked up a second pollinarium. Our observations and analyses suggested that morphological interactions between flower and pollinator are crucial to the success of pollination and to prevent self-pollination and thus that pollinarium reconfiguration is unnecessary in shelter deceptive orchids, such as Serapias species, for the promotion of cross-pollination. Serapias represent a case of interactions between plant and pollinator; the formation of the tubular shape of the flower is an essential preadaptation for the development of resting site mimicry originating exclusively in Serapias among Mediterranean orchids.

Sweet as Vanilla hartii: Evidence for a nectar-rewarding pollination mechanism in Vanilla (Orchidaceae) flowers

Little is known about the pollination mechanisms of species belonging to the genus Vanilla (Orchidaceae). Both autonomous self-pollination and animal-mediated pollination mechanisms seem to exist amongst the Vanilla species, yet few studies provided real evidence on pollination events. The aim of this study was to better understand the pollination mechanism of Vanilla hartii. Four V. hartii populations were selected within our study area in southern Costa Rica to observe pollination events and identify the natural pollinators of this Neotropical Vanilla species. We tested for nectar presence, analysed nectar composition, and examined floral fragrances. Furthermore, we identified floral visitors and documented their behaviour, quantified fruit set during two years, and compared morphological traits of flowers and their visitors. Sampled flowers contained 1.85 ± 1.07 µL nectar that averaged 34.79% sugar, dominated by sucrose. We observed orchid bees belonging to the genus Euglossa entering the tube formed by the labellum to search for nectar, indicated by their extended proboscis and prolonged visits, some of which exited the labellar tube with pollen masses attached to their scutellum. Combining our behavioural and phytochemical data, we demonstrate the presence of a nectar-rewarding pollination mechanism in the genus Vanilla that shows a higher natural fruit set compared to deceptive Vanilla species. An overview of the pollination mechanisms known so far provides insights into the potential evolution of reproductive strategies within this commercially important orchid genus.

Pollinaria Reconfiguration Mechanism of Widespread Euro-Mediterranean Orchids: The Effects of Increasing Air Temperature.

Orchids are fascinating for many reasons: their reproductive strategies, their pollination systems and the various morphological adaptations they have evolved, including the presence of pollen grains agglomerated into two masses, called pollinia, which form a structure known as a pollinarium. After withdrawal from a flower, the pollinarium undergoes a bending movement such that the pollen masses become correctly orientated to strike the stigma. We evaluated the duration of pollinator visits to inflorescences and the effects of temperature on pollinaria reconfiguration in eight orchid species in order to analyze the effects of increasing air temperature on the changes in bending time, and thus on geitonogamy levels. The impact of temperature on insect behavior was not assessed because our priority was to understand the effects of temperature on the process of pollinaria reconfiguration. All the examined species showed natural reconfiguration times that were 1.7–3.0 times longer than the pollinator residency times. A higher temperature showed a reduction in bending time regardless of the species tested. However, the bending time was never shorter than the residence time of the insects on the flower. Our data showed that high temperatures had a limited effect on the pollinarium reconfiguration time, thus indicating that high temperatures had a limited effect on folding compared to the effect that it had on the viability of the pollen.

Descrição biométrica da espécie Trigona truculenta (Hymenoptera: Apidae) e transferência de nidificação em Belterra, Pará

The stingless bee Trigona truculenta, popularly known as "Sanharão" occurs in the Neotropical region and is considered a defensive bee, because it has an expressive population, with approximately 80,000 individuals, who have cutting jaws and defend themselves from their invaders with "bites ", Making management difficult. In this sense, the present work had the objective of performing the rescue and transfer of a nesting nest in an urban area of the municipality of Belterra, Pará, as well as to study the habit of nesting, providing subsidies for management programs and preservation of colonies of native bees. Information about the nest number and area of breeding discs, calving cell size (height, diameter), size of honey pots and pollen, volume of honey pots and weight of the pollen masses contained in the pots. The species has a very large nest structure, which size was 1.30 m long by 1.25 m wide, requiring considerable space for nesting, being able to be rescued and managed rationally for environmental conservation units. The nest was divided into six boxes, five with their breeding discs with real cells and princesses and a box with breeding discs and queen. These boxes were taken to an area of environmental preservation (APA). It was concluded that it is necessary to redeem species of native bees that do not present the potential for rational breeding, because they run the risk of destroying their swarms, causing an imbalance to the environment, since they provide an indispensable service, pollination.

Fluid Dynamics of Hydrophilous Pollination in Ruppia (widgeon grass)

The aim of this work is to understand the physics underlying the mechanisms of two-dimensional aquatic pollen dispersal known as hydrophily. We observed two mechanisms by which the pollen released from male inflorescences of Ruppia is adsorbed on a water surface. Adsorbed pollen masses then combined under the action of capillary forces to form pollen rafts. This increases the probability of pollination since the capillary force on a pollen raft toward a stigma positioned at the water surface is much larger than on a single pollen grain.

Kin selection and the evolution of plant reproductive traits.

Competition among developing seeds and sibling rivalry within multiovulated ovaries can be deleterious for both the maternal parent and the siblings. Increased genetic relatedness of seeds within the ovary may foster kin selection and reduce the deleterious consequences of sibling competition. The pollen parent may also be selected for siring all progeny within a fruit. I propose a series of hypotheses to explain the evolution of a number of reproductive traits in angiosperms in the context of kin selection and sibling rivalry within the ovaries of angiosperms. I present evidence to show that a single-pollen parent, indeed, often sires seeds within multiovulated ovaries. Various types of pollen aggregations and transfer of such pollen masses to the stigmas of flowers by specialized pollinators make this increased genetic relatedness possible. An alternative mode to reduce sibling rivalry may be the reduction of ovule number to one, an evolutionary trend that has independently occurred many times in flowering plants. Finally, I build on previously established correlations to predict two sets of correlations among reproductive traits. In the first case, large showy flowers, transfer of pollen en masse by specialized pollinators, and multiovulated ovaries and multisided fruits seem to be correlated. In the second case, the previously established correlations among small and inconspicuous flowers, pollination by wind, water or generalist insects, flowers and fruits with few or single ovules and seeds, respectively, may also include monoecy or dioecy. Although correlations among many of these traits have been established in the past, I invoke kin selection and sibling competition to explain the evolution of correlated traits as two distinct evolutionary pathways in angiosperms.

Timing and size of daily pollen meals eaten by adult females of a solitary bee (Nomia melanderi) (Apiformes: Halictidae)

Pollen feeding by solitary bees has been studied mainly with their larvae, overlooking pollen feeding by adults. To address this knowledge gap, we determined the amounts and temporal (daily and lifetime) schedules of pollen consumption by freely nesting, adult females of the alkali bee (Nomia melanderi, Halictidae). Nesting females of known ages were taken at different hours of the day from nesting aggregations managed for alfalfa pollination in southeastern Washington State (USA). Each dissected bee was visually scored for pollen fill of the crop, midgut, and hindgut; we also quantified the crop’s pollen capacity. Our dissections of 188 bees show that adult females ate pollen daily for at least the first 2 weeks following emergence. Most bees (85 %) had pollen boluses in one or more gut regions, indicating active pollen feeding. Pollen masses were most likely in the midgut; the daily volume consumed usually filled both the crop and midgut at least once. Full crops contained 34,000 alfalfa pollen grains, equivalent to <20 % of a full scopal load and 0.8 % of the pollen in a nest provision. Proportionately more females ate pollen as the day progressed, indicated by pollen masses in the crop. By early evening, crops of all bees were filled with pollen. Our study reveals the dietary importance of regular pollen feeding for nesting adult female solitary bees, and not just their larvae, with implications for bee foraging ecology, dietary physiology, reproduction, toxicology, and pollination ecology.

Floral miniaturisation and autogamy in boreal-arctic plants are epitomised by Iceland's most frequent orchid, Platanthera hyperborea.

Background and Aims. This paper concludes our series of publications comparing island and mainland speciation in European butterfly-orchids, by studying the morphology, phylogenetics and reproductive biology of the controversial circum-arctic species Platanthera (Limnorchis) hyperborea—the most frequent of seven Icelandic orchids. We draw particular attention to its phylogenetic placement, remarkable reproductive biology and morphological convergence on other Platanthera lineages through floral miniaturisation.Methods. Five populations of P. hyperborea in southwest Iceland were measured for 33 morphological characters and subjected to detailed multivariate and univariate analyses, supported by light and scanning electron microscopy of selected flowers. Representative samples from six populations were sequenced for nrITS and placed in a taxonomically broader phylogenetic matrix derived from previous studies.Key Results . Section Limnorchis consists of three distinct ITS-delimited clades based on P. stricta, P. sparsifolia–limosa–aquilonis and P. dilatata–hyperborea. Within the latter group, supposed species boundaries overlap; instead, the data indicate a crude stepwise series of ribotypic transitions extending eastward from North America to Iceland. Morphometric data failed to identify any taxonomically meaningful partitions among Icelandic P. hyperborea populations, despite the presence of a distinct and apparently plesiomorphic ribotype at the most glacially influenced habitat sampled. Microscopic study of the flowers revealed several distinguishing features (some not previously reported), including resupinate lateral sepals, toothed bract margins, club-shaped papillae shared by both the interior of the labellar spur and the stigmatic surface, and an exceptionally adhesive stigma that is reliably covered in disaggregated pollen masses prior to anthesis; auricles are absent.Conclusions. Ribotypes suggest that Icelandic P. hyperborea represents the terminus of a migration route that may have begun in East Asia before passing through North America and presumably Greenland. The incohesive pollinia, rapidly desiccating anther locules, weakly developed rostellum, exceptionally adhesive stigma and the close juxtaposition of compact male and female reproductive organs together conspire to cause routine autogamy and frequent cleistogamy, despite the continued production of substantial nectar reservoirs in the spur and consequent ongoing attraction to the flowers of insects, including mosquitoes. When considered in combination with independently derived lineages of Platanthera on the Azorean and Hawaiian archipelagos also bearing small green flowers, our observations show allometric and paedomorphic reductions in flower size as the primary evolutionary driver, but also indicate strong developmental and functional constraints.

VARIABILITY of FOOD STORES of TETRAGONISCA FIEBRIGI (SCHWARZ) (“RUBITA” OR “RUBITO”) (APIDAE, MELIPONINI) from the ARGENTINE CHACO BASED on POLLEN ANALYSIS

Fil: Vossler, Favio Gerardo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro de Investigaciones y Transferencia de Entre Rios. Universidad Nacional de Entre Rios. Centro de Investigaciones y Transferencia de Entre Rios; Argentina

Nesting biology of an Oriental carpenter bee, Xylocopa (Biluna) nasalis Westwood, 1838, in Thailand (Hymenoptera, Apidae, Xylocopinae)

The biological study of wild non- Apis bees can provide useful information that may help with the pollination of food crops and native plants in areas where the keeping of honey bee colonies is restricted or affected by CCD. Here, we describe the nesting biology of the Oriental large carpenter bee, Xylocopa (Biluna) nasalis Westwood, 1838. An aggregation of more than 80+ bamboo nests of X. nasalis was discovered in Suan Pheung district, Ratch Buri province, Thailand on the 25 th of May 2012. We collected 27 nests from the site to dissect, measure the external and internal nest architecture, and analyze the pollen composition of the pollen masses. X. nasalis constructs linear unbranched nests with nest entrance mostly located at the open-end of the bamboo culms. The nest length and the branch diameter of the nest entrance (excluding nesting edge) are 25.40 ± 6.95 cm and 17.94 ± 6.00 mm, and the maximum number of provisioned cells is 8. A biased sex ratio of 8♀: 1♂ is reported, with up to 7 adults inhabiting in a single nest. 29 pollen types were identified from 14 pollen masses using an acetolysis method and visualization under both light microscope and scanning electron microscope. 13 pollen types were considered as major pollen sources (contribute ≥ 1% in total pollen volume); however, only 10 can be identified to family and generic levels. The dominant pollen sources are of the families Elaeagnaceae ( Elaeagnus cf. latifolia), Euphorbiaceae (Croton), Fabaceae (Senna siamea and Cassia), Fagaceae (Lithocarpus and Castanopsis), and Lythraceae (Trapa) which are mostly native to the region of Southeast Asia. The nesting architectural details should prove to be beneficial to beekeepers and researchers who are interested in trapping and studying X. nasalis, and the polylectic behavior of X. nasalis can be highly valuable for future crop pollination strategies, particularly for plants that require sonication of their poricidal anthers.

Small pollen grain volumes and sizes dominate the diet composition of three South American subtropical stingless bees

The pollen preferences of three Meliponini species (Geotrigona argentina, Scaptotrigona jujuyensis and Tetragonisca fiebrigi) were studied in the Chaco forest of South America. Surprisingly, a large number of pollen types with small volumes and size were found in pollen masses stored in the 18 nests studied. Small pollen grains are commonly found in small flowers with short pistils, a flower morphology adapted to the pollination by these small- to medium-sized bees. The prevalence of grains with small volumes may be due to the preference of Meliponini bees for small flowers with short pistils, supporting a previously suggested hypothesis of diffuse co-evolution between mass-flowering trees and these tiny bees in Neotropical habitats. However, the opportunistic foraging habit of these generalist bees would suggest that the large number of grains with small size is due to their greater availability in the Chaco forest nearby the nests. This study also provides measurements and descriptions of pollen cytoplasmic shapes as well as a new classification of pollen volumes based from measurements of the five pollen size categories using non-acetolyzed grains.

Plants &amp; fungi: Bent tissue strip gives orchid kick: Study dissects how plants hit bees with pollen masses

Science NewsVolume 176, Issue 5 p. 13-13 In The News Plants & fungi: Bent tissue strip gives orchid kick: Study dissects how plants hit bees with pollen masses Susan Milius, Susan MiliusSearch for more papers by this author Susan Milius, Susan MiliusSearch for more papers by this author First published: 09 October 2009 https://doi.org/10.1002/scin.5591760516AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume176, Issue529 August 2009Pages 13-13 RelatedInformation

Moth pollination of Metaplexis japonica (Apocynaceae): pollinaria transfer on the tip of the proboscis

Asclepiad pollinaria (including pollen masses) attach to diverse body parts of flower visitors in many ways. In this paper, we observed nocturnal moths (Lepidoptera: Pyralidae and Noctuidae) transporting the pollinaria of the Japanese species Metaplexis japonica (Thunb.) Makino (Apocynaceae: Asclepiadoideae) on the tip of the proboscis. Flowers of this species may induce nectar-feeding moths to pull out the proboscis along a guide rail (anther slit), thus clipping the pollinaria onto the tip of the proboscis and transferring the pollinaria to the next flower. The transfer of pollinaria on the unique vector of a moth proboscis tip is an interesting pollination mechanism among previously reported entomophiles.

CONIFER POLLEN CONES FROM THE CRETACEOUS OF ARKANSAS: IMPLICATIONS FOR DIVERSITY AND REPRODUCTION IN THE CHEIROLEPIDIACEAE

Abstract Cheirolepidiaceous conifer pollen cones (Classostrobus arkansensis new species) from the Lower Cretaceous (Aptian/Albian) Holly Creek Formation of Arkansas, some still attached to Pseudofrenelopsis parceramosa Fontaine, shoots, bear helically arranged, semipeltate to dorsiventral microsporophylls with abaxially situated pollen masses. The in situ Classopollis Pflug, 1953 pollen and orbicule outer sculpturing consists of short spinules. The abaxial epidermis of the microsporophyll head consists of a stomatiferous central region of isodiametric cells bearing hollow papillae with rounded apices and a nonstomatiferous marginal area of elongate, nonpapillate cells. The head abaxial cuticles are thin relative to those of the shoot internodes. A cutinized hypodermis is lacking. Previously described pollen cones of Classostrobus comptonensis (Alvin et al., 1994) from the English Wealden (Barremian) are also associated with P. parceramosa shoots; however, they differ substantially from the Arkansas cones ...

Nesting Biology of a Neotropical Bee, Ceratina mexicana currani Schwarz (Hymenoptera: Apidae: Xylocopinae)

Ceratina Latreille is a large cosmopolitan genus of usually small and slender bees that nest in pithy dead stems or twigs (Michener, 2000). Some species facultatively develop small social colonies of adults and food transfers (trophallaxis) among nestmates can occur (reviewed in Michener, 1990). Although Ceratina is taxonomically diverse in the tropics, the biology of Neotropical species is, in general, still poorly known. Herein we present notes on the nesting biology and floral resources of Ceratina mexicana currani Schwarz from Barro Colorado Island (BCI, Republic of Panam?). This species belongs to the Neotropical subgenus Calloceratina and was previously known from the holotype collected at the same locality (Schwarz, 1934; Michener, 1954). So far, the only information known on the biology of Calloceratina is the brief notes on the nest architecture of two different species by Friese (1925). Nest architecture: The first nest of C mexicana currani was discovered at the end of the dry season (May 20, 2001). The nest was inside a dead, dry pithy stick of ~2 cm in diameter and consisted of an unbranched tunnel that ran along the axis of the stick. The nest entrance was rounded with 6.7 mm in diameter and the tunnel was 16 cm in length, with a diameter ranging from 5.3 to 5.7 mm. There were 8 female pupae inside the tunnel; the innermost pupa was totally pigmented in contrast with the outermost which was weakly colored. One of the fully colored pupae was covered with mites. Cell partitions were absent and pupae were in contact with each other. The inner walls of the tunnel were cleaned of feces. In addition to the pupae, four adult females were found. A second nest was found at the beginning of the dry season (20 February 2002). The nest was within a dry stick of ~1.3 cm in diameter, and was found at a 40? angle to the vertical, 140 cm above the soil. The entrance was rounded and constricted but not constructed (diameter = 4.6 mm) at the tip of the stick. The tunnel enlarged gradually in diameter from the entrance (6 mm) to its end (6.8 mm), and was 87 mm in length from the nest entrance to the top of the first cell. The nest had three sealed cells?the innermost cell contained a medium-sized larva; the next one a small larva, and the outermost, an egg (Fig. 1 A). The cells were excavated, unlined, and had approximate lengths of 13 mm (n = 1) and a diameter of ?4.8 mm (n ? 2). Pollen masses, as reported for other Ceratina (Michener and Eickwort, 1966; Michener, 1990), were attached to one side of the cell, somewhat rectangular, semiliquid and had a strong odor. Larvae and eggs were attached to the lower parts of the pollen masses. Partitions between cells were made of compressed sawdust, concave below and convex on top, with a small hole (~1 mm) in the center (Fig. IB). A single adult female was found in this nest. Host plants: Pollen grains from eight plant species belonging to eight families were found within brood provisions of the second nest of C. mexicana currani (Table 1). In all cases, 95-100% of pollen within each brood cell was from a single species, Chamaesyce sp. (Euphorbiaceae). The remaining species were present in trace amounts (<1% of the total per cell). Trophallaxis: Six pupae from the first nest were reared to emergence and the adults paired in small tube-like cages, separated by fine screening, allowing them to touch mouthparts through the screen as explained in Wcislo and Gonzalez (in press). One bee of each pair was fed with a mixture of colored honey and water. The unfed bees lived for 10, 12 and 20 days and had colored stomachs when dissected under the microscope, indicating that food transfer had occurred. Taxonomic comments: Unlike Schwarz's holotype of C. mexicana currani, the yellowish spot on the clypeus of our specimens is larger, reaching the level of the tentorial pits, and rather trapezoidal to bell-shaped. One of them also differs slightly from the holotype by having a single row of punctures lateral to each parapsidal line on the mesoscutum and rather scattered punctures on the lateral sides of the genae. The holotype has a small, rather

Lepidopteris callipteroides, an earliest Triassic seed fern of the Sydney Basin, southeastern Australia

Earliest Triassic shales in the Coal Cliff Sandstone, Caley Formation, Widden Brook Conglomerate and Dooralong Shale (all basal Narrabeen Group) of the Sydney Basin contain a low diversity fossil flora that survived the greatest mass extinction of all time at the Permian-Triassic boundary. Only one species of seed fern is known from this flora and its affinities were unclear until discovery of its reproductive organs and complete large leaves. An ovuliferous reproductive organ, Peltaspermum townrovii sp. nov., can be attributed to the same plant as the leaves because of their identical stomatal apparatus, which is cyclocytic with papillae overhanging the stomatal pit. Polleniferous organs, Permotheca helbyi sp. nov., may have belonged to the same plant, but are only linked by evidence of association on the same bedding plane yielding no other gymnosperms. Pollen masses found within the polleniferous organ include grains identified as Falcisporites australis (de Jersey) Stevens (1981) when found dispersed. The leaves of this plant have long been enigmatic and attributed to ‘Thinnfeldia’ callipteroides or ‘Dicroidium’ callipteroides; however, these genera had very different cuticular structure. Reassessment of the frond architecture of this plant, based on a large, nearcomplete specimen together with information from cuticles and ovuliferous organs, allows reassignment to Lepidopteris callipteroides (Carpentier) comb. nov. The remarkable cuticle thickness, small stomatal size and low stomatal index of these leaves reflect a time of unusually high atmospheric concentrations of carbon dioxide. This plant was an invader of the Sydney Basin from northern Gondwana, spreading southward during the post-apocalyptic earliest Triassic greenhouse.

A survey of the function of the lethal kettle traps of Arisaema (Araceae), with records of pollinating fungus gnats from Nepal

Evidence from recent research combined with an evaluation of the literature indicates thatArisaema is adapted to pollination by fungus gnats. It apparently shares this peculiarity among aroids only with the distantly related genus Arisarum. In addition to previous records from Japan and North America, systematic collections from nine Arisaema species during several expeditions in the Himalayas in Nepal showed that, although other less efficient insect groups may participate, the nematoceran families Mycetophilidae and Sciaridae are the principal pollen vectors; they best fit the pollination apparatus of the mainly (para)dioecious kettle trap blossoms. A total of 16 fungus gnat genera (both Mycetophilidae and Sciaridae) comprising 47 identified species (among them one genus and 22 species new to science) were observed. Usually members of more than one taxon are attracted per Arisaema species, and both sexes of gnats are involved. Visitor sets differed to some degree, depending on host species, area, and altitude; they do not, however, represent the complete fungus gnat fauna of a region. Relevant traits of growth habit and inflorescence structure are surveyed, and a detailed description of the pollination process is given, based on observations made on specimens cultivated in Europe, where vicariant fungus gnats are the pollinators. Attraction is deceptive by mimicking olfactory, visual and tactile cues characteristic of fungi where the gnat sexes normally meet and females oviposit. Odours produced by osmophores (the spadix appendage or spathe tip) play the most important part. The identified volatile compounds are mainly short-chained aliphatic aldehydes and alcohols. Flagelliform osmophores of some species, up to several dm long, reach the substrate and serve as conducting paths. Gnats become imprisoned when they inadvertently slide down the inner wall of the spathe tube. Its surface including the spadix is covered with ablative wax particles that inactivate the insects» tarsal pulvilli. This gliding device, in some species reinforced by zones of imbricate papillae, is irreversible, and no movements of floral parts allowing escape via the spathe mouth occur. Anthesis lasts several weeks. In the male spathes, victims are forced to wade through the pollen masses that have accumulated at the spathe's bottom; there they find an exit hole formed by local gaping of the spathe rims. The female spathes lack such an aperture. After potentially depositing pollen on the stigmas during their efforts to escape, gnats are detained until death. Except for an autogamous subspecies of A. flavum Schott, the few monoecious taxa of Arisaema are protogynous and possibly self-sterile. In monoecious A. tortuosum (Wall.)Schott, exit forming is delayed until pollen release. Three Arisarum species that are suspected to deviate in their floral syndrome are discussed along with araceous genera possessing similar one-way pitfall mechanisms.

A survey of the function of the lethal kettle traps of Arisaema (Araceae), with records of pollinating fungus gnats from Nepal

Abstract Evidence from recent research combined with an evaluation of the literature indicates that Arisaema is adapted to pollination by fungus gnats. It apparently shares this peculiarity among aroids only with the distantly related genus Arisarum . In addition to previous records from Japan and North America, systematic collections from nine Arisaema species during several expeditions in the Himalayas in Nepal showed that, although other less efficient insect groups may participate, the nematoceran families Mycetophilidae and Sciaridae are the principal pollen vectors; they best fit the pollination apparatus of the mainly (para)dioecious kettle trap blossoms. A total of 16 fungus gnat genera (both Mycetophilidae and Sciaridae) comprising 47 identified species (among them one genus and 22 species new to science) were observed. Usually members of more than one taxon are attracted per Arisaema species, and both sexes of gnats are involved. Visitor sets differed to some degree, depending on host species, area, and altitude; they do not, however, represent the complete fungus gnat fauna of a region. Relevant traits of growth habit and inflorescence structure are surveyed, and a detailed description of the pollination process is given, based on observations made on specimens cultivated in Europe, where vicariant fungus gnats are the pollinators. Attraction is deceptive by mimicking olfactory, visual and tactile cues characteristic of fungi where the gnat sexes normally meet and females oviposit. Odours produced by osmophores (the spadix appendage or spathe tip) play the most important part. The identified volatile compounds are mainly short-chained aliphatic aldehydes and alcohols. Flagelliform osmophores of some species, up to several dm long, reach the substrate and serve as conducting paths. Gnats become imprisoned when they inadvertently slide down the inner wall of the spathe tube. Its surface including the spadix is covered with ablative wax particles that inactivate the insects» tarsal pulvilli. This gliding device, in some species reinforced by zones of imbricate papillae, is irreversible, and no movements of floral parts allowing escape via the spathe mouth occur. Anthesis lasts several weeks. In the male spathes, victims are forced to wade through the pollen masses that have accumulated at the spathe's bottom; there they find an exit hole formed by local gaping of the spathe rims. The female spathes lack such an aperture. After potentially depositing pollen on the stigmas during their efforts to escape, gnats are detained until death. Except for an autogamous subspecies of A. flavum Schott, the few monoecious taxa of Arisaema are protogynous and possibly self-sterile. In monoecious A. tortuosum (Wall.)Schott, exit forming is delayed until pollen release. Three Arisarum species that are suspected to deviate in their floral syndrome are discussed along with araceous genera possessing similar one-way pitfall mechanisms.

Secondary and tertiary pollen presentation in Polygala myrtifolia and allies (Polygalaceae, South Africa)

In Polygala myrtifolia and probably other South African Polygala species with asymmetrical flowers, pollen is first presented in a very unusual manner; eight sausage-like pollen masses are attached by their ends to the crook-shaped tip of the style (secondary pollen presentation). Floral morphology suggests that when the asymmetrical keel of the flower is pressed down by a sufficiently strong bee, the pollen presenter springs out and the stigma and pollen hit the visitor dorsally on the right flank pleuro-nototribic. When the keel returns to its original position, the remaining pollen is moved into the rostrum of the keel. In subsequent visits pollen is squeezed out of there by a pocket at the tip of the style. This tertiary pollen presentation follows the piston mechanism and dusts the ventral side of the visitor (sternotribic).

Trophic aspects of caste determination in Halictus ligatus, a primitively eusocial sweat bee

Caste determination in primitively eusocial sweat bees is thought to be due to an interacting suite of factors, including size of the larval provision mass, time of year, and social context of the nest into which a young female emerges. Newly emerged gynes are significantly fatter than newly emerged workers, suggesting the existence of larval caste determination cues. Since photoperiod, temperature, and interactions with nestmates were unlikely to affect larval caste determination, we compared the sizes and contents of larval provision masses destined to produce either workers or gynes. Gyne-destined larvae consumed pollen masses that were larger and contained slightly more sugar than those of worker-destined larvae. We suggest that sugar content is one cue which prompts the development of fat reserves in gyne-destined females but not in worker-destined females. The amount of fat possessed by a newly emerged female influences her chances of successfully entering diapause shortly after emergence. Therefore, small, lean females may be more susceptible to behavioural control by queens and more likely to become workers, while large, fat females would be more likely to become gynes.